Christmas is a very important holiday in the Greek Orthodox Church, and it is celebrated on a different date than in the Western Church. In the Greek Orthodox Church, Christmas is celebrated on January 7th, which is 13 days after Christmas in the Western Church. This date is based on the Julian calendar, which was used by the Roman Empire until the 16th century. The date of Christmas in the Greek Orthodox Church is also determined by the date of the Annunciation, which is March 25th in the Orthodox Church.